The present invention relates to an exterior component attached to a lower part of a vehicle body, such as a fender liner and an under protector that are attached to the lower part of the exterior of vehicle body.
Generally, exterior components such as fender liners and under protectors cover are attached to the lower part of a vehicle to protect the bottom from soiling of rain water and mud, and scratches by thrown up pebbles and gravel. In terms of guaranteeing a sufficient rigidity that endures soiling and scratches, such exterior components are made hard using materials such as synthetic resin and synthetic rubber. However, such a hard exterior component produces impact noise (chipping noise) when hit by rain water, mud, grave, and pebbles. Such chipping noise is propagated to the passenger compartment. Thus, such a hard exterior component does not contribute to improvement of quietness in the passenger component, and can be the source of noise in some cases.
To reduce such chipping noise, for example, Japanese Laid-Open Patent Publication No. 2000-264255 discloses a fender liner that is made of a hard fiber plate. The hard fiber plate is formed by bonding fibers with binder, fusion bonding fibers with hot melt resin powder, or heat fusion bonding the mixture of fibers and lower melting point fibers. Japanese Laid-Open Patent Publication No. 2000-264255 discloses that a fender liner made of hard fiber plate is light and has cushioning property, and therefore reduces pitching noise since it softens the impact of collision of dirt, pebbles, and water.
Other than pitching noise, noises that are propagated to the passenger compartment include pattern noise. Pattern noise refers to scratching noise produced by contact between treads (parts that contact the road surface) of tires and the road surface when the vehicle is moving.
To reduce the propagation of noise such as the above described chipping noise and pattern noise to the passenger compartment, for example, Japanese Laid-Open Patent Publication No. 2004-142675, Japanese Laid-Open Patent Publication No. 2004-299626, and Japanese Laid-Open Patent Publication No. 2004-359066 each discloses an exterior component made of sheet material containing nonwoven fabric. Nonwoven fabric is formed by physically intertwining a number of fibers, or tying a number of fibers with binder. An exterior component formed of a sheet material containing such nonwoven fabric has minute spaces (cells) surrounded by intertwined fibers. The cells absorb noises such as pattern noise and chipping noise, thereby reducing the propagation of noises to the passenger compartment. Japanese Laid-Open Patent Publication No. 2004-359066 discloses that a sheet material has a laminated structure of a plurality of stacked layers, and each of the layers has a different function.
In recent years, there is an increasing demand for quietness in vehicle passenger compartments. This trend is applied to all sorts of vehicles. Particularly, the trend is noticeable in hybrid vehicles and fuel cell vehicles, which have been developed in view of minimizing damage to the environment. To meet such needs, latest vehicles tend to have a function to reduce noise produced by power source such as an internal combustion engine and an electric motor, and power transmission system. In addition to reduction of noise produced in such vehicle drive systems, reduction of noise audible in the passenger compartment is an important challenge.
Noises audible in the passenger compartment include road noise in addition to above mentioned chipping noise and pattern noise. Road noise is a muffled noise that is produced when vibration of wheels is transmitted to the vehicle body through suspensions and the vibration of the vehicle body vibrates the air in the passenger compartment. The sources of chipping noise, pattern noise, and road noise cannot be easily removed. Therefore, to reduce audible noise in the passenger compartment, vibration of the vehicle body caused by chipping noise, pattern noise, and road noise needs to be suppressed.
To further reduce noise, the fender liner disclosed in Japanese Laid-Open Patent Publication No. 2000-264255 may be modified to increase the cushioning property, thereby reducing the impact of hitting dirt, pebbles and water (chipping). However, increase in the cushioning property is expected to lower the rigidity. Accordingly, the endurance against is predicted to be lowered. Further, although Japanese Laid-Open Patent Publication No. 2000-264255 discloses reduction of chipping noise, the publication neither disclose nor suggests reduction of scratching noise and muffled noise such as pattern noise or road noise. On the other hand, although Japanese Laid-Open Patent Publication No. 2004-359066 discloses that the sound absorption effect is increased as the number of the cells is increased, a mere increase in the number of cells may reduce the rigidity. Thus, the durability against chipping is predicted to be lowered. Therefore, it is difficult to design an exterior component that satisfies both demands related to the noise reduction capability and the durability against chipping.
In exterior components having nonwoven fabric as disclosed in the above publications, water derived from rain and snow can enter the cells and taken in. An exterior component that has absorbed water increases its weight by the weight of the absorbed water. The increase in the weight can be a cause of deflection and deformation, and reduce the attachment strength of the exterior component with respect to the vehicle body. That is, the rigidity of an exterior component containing nonwoven fabric is sufficient in a normal state, or in a dry state, but insufficient for enduring the increase in weight due to absorbed water. Accordingly, Japanese Laid-Open Patent Publication No. 2004-142675 discloses an exterior component having a water repellent portion so that water does not easily collect on the surface of the exterior component.
However, in the case of an exterior component that contains nonwoven fabric, providing such water repellent portion is not sufficient for completely preventing absorption of water. That is, such a water repellent portion is capable of preventing water that temporarily collects on the surface of the exterior component from being absorbed by the component. However, as for water that is thrown up by a wheel and smashes against the exterior component, and water that stays on the component, the water repellent portion cannot sufficiently suppress such water absorption by the component. To prevent the absorption of water completely, the cells may be blocked. If this is the case, however, sound absorption effect of the cells cannot be obtained. Thus, there is no point in using nonwoven fabric as a material for the exterior component. Therefore, in the case of an exterior component containing nonwoven fabric, it is difficult to eliminate absorption of water and problems caused by such water absorption, while maintaining the sound absorption effect of the cells.